The invention relates to anti-jamming apparatus and method for radar. It also relates to a radar system equipped with such a device.
Modern military aircraft are usually equipped with jammers which emit noise signals within the frequency range of the radar systems capable of detecting their presence. Ground radars receiving these high-power signals, even on a minor lobe, are saturated and blinded.
A solution of the prior art for overcoming this disadvantage and compensating the active jamming noise involves using auxiliary antennas of sufficient numbers, in principle one for each jammer.
The signal field received by each auxiliary antenna is weighted in terms of amplitude and phase by means of a complex coefficient and is then added to the signal field received by the main antenna, so as to form a resultant signal field. Several known methods operating either in an open loop or in a closed loop make it possible to select the value of the complex coefficients correctly, so as to cancel the component of the said resultant field which arises from the jammers: this component is the sum of the field received by the main antenna and the weighted field received by each of the auxiliary antennas.
This known solution has the following disadvantages:
The auxiliary antennas cannot be very directional for reasons of bulk, because of their numbers, these being limited, moreover.
The anti-jamming principle used in this solution gives rise to a general raising of the diffuse pattern resulting from the linear combination of the fields received by the main and auxiliary antennas.
The number of jammers handled is limited by the number of auxiliary antennas: the arrival of a new jammer disturbs operation, since it cannot be handled and since it very likely arrives in a direction in which the diffuse pattern of the compensated antenna is considerable.